(1) Field of the Invention
The present invention relates to a flat visible display device and to a method of forming a picture using that device.
(2) Related Art
U.S. Pat. No. 4,719,388 contains a detailed description of visible display device. FIGS. 1 and 2 substantially conform to the figures of the same number as set forth in the aforesaid patent. The display device 100 of FIGS. 1 and 2 does not show external components such as a housing. The inside of display device 100 is maintained at a high vacuum atmosphere. In the construction of such a display device, a backing electrode 2 is located behind cathode wires 4 in a plane adjacent to, and parallel with, a backing plate 1 which may possibly provide support for the backing electrode. Bias voltage Vbe is applied to backing electrode 2.
Cathode wires 4 (more fully described with reference to FIG. 2) are disposed at a predetermined interval from the backing electrode 2 to be supplied with cathode voltage VK.
Accelerating electrodes 5 are arranged in a lattice configuration (see FIG. 2) are disposed at a predetermined interval from the cathode wires 4, so that an accelerating voltage Vacc can be applied thereto.
A face plate assembly 12 is disposed at the top and at the opposite end of the display device 100 from backing plate 1, and includes a face plate 11, a phosphorescent screen 10, and an anode electrode 9.
An anode voltage is, of course, applied to the anode electrode so that electrons impact on the phosphorescent screen 10, whereby a picture is displayed on the face side 11' of face plate 11.
An address plate 13, comprising a plurality of first and second addressing electrodes 6,8, respectively, orthogonally positioned with respect to substrate 7 of the address plate 13 (see FIG. 2), is interposed between the accelerator electrodes 5 and the face plate assembly 12. The first address electrodes 6 are shown extending in one direction on the one face of substrate 7 and second addressing electrodes 8 extend in a direction perpendicular thereto on the opposite face of the substrate 7. The first and second addressing electrode 6,8 is supplied with bias voltages Vfe,Vse, respectively.
During the operation of flat visible display device 100 constructed as described above, space-charge cloud of free electrons 3,3' is established as shown by the dotted line in FIG. 1.
During blanking of the display device, the cathode wires 4 are supplied with cathode voltage Vk to emit electrons. Thermal electrons are emitted to the backing plate 1 from a space-charge cloud of free electrons 3 induced by negative voltage applied to the backing electrode 2. Thermal electrons emitted to the accelerator electrode 5 establish a space-charge cloud 31 of free electrons between the address plate 13 and accelerating electrode 15.
The speed and direction of the space-charge cloud 3' of free electrons is controlled under the influence of the bias voltages vbe,Vk,Vfe,Vse.
The brightness of the screen is determined by the number of electrons striking the phosphor layer 10. However, a conventional flat visible display device has a short creation time of space-charge cloud 3' which corresponds to the blanking time, so that a sufficient number of electrons can not be obtained.
Furthermore, even with an efficient screen driving signal, a small number of electrons are emitted from the wire cathodes 4 because of the electric field effect. At that time, these electrons strike the phosphor layer 10 such that there is a higher brightness than that at its surroundings. Thus, in practice, non-uniform brightness of the line type corresponding to the cathode arrangement is formed on the screen.